Implantable devices such as cardiac sensors, pacemakers, and defibrillators normally have a main housing implanted in a patient's pectoral or abdominal region. A flexible lead having one or more electrical conductors extends internally from the housing to the patient's heart. In a typical application, the lead is inserted endocardially, extending from the housing through an incision in a major vein, through the vein, and into the chamber of the heart. A sensor on the distal end of the lead may contact the cardiac tissue for sensing and stimulating the tissue.
The surgical process of inserting and positioning the lead requires skill and precision, and is typically performed by inserting the lead alone without the housing attached. Guiding the lead through the venous system may also require the insertion of stylets in a hollow lumen of the lead, as accessed from the proximal end. Therefore, detachable and reattachable leads are normally used, with the leads being connected to the housing after proper insertion and placement. The connection process occurs during surgery, after lead insertion and before housing implantation. Therefore, it is desirable that the connection process be achieved quickly, and with a high degree of confidence that a proper connection has been made.
In existing apparatus, the lead has an elongated male proximal end lead connector that is received by an elongated bore defined in a header portion of the housing, with the electrical and mechanical connection being made deep within the bore of the header. Although the header portion may be somewhat transparent in the prior art, the small size of miniature connectors makes difficult the confirmation of proper insertion by viewing through the header material. The trend toward miniaturization of implantable devices only exacerbates this problem. Also, any new superior biocompatible materials with poor optical qualities would be unusable for such a header.
The surgeon may also rely on the apparent insertion depth or tactile feel to infer proper connection. However, this method has drawbacks since the lead connectors may give the illusion of being fully inserted when they are not, such as if a lead's sealing ribs are not adequately lubricated to slide readily into the bore, or if the lead becomes caught on a misaligned or misdimensioned part, or if a foreign particle interferes with the connection. An improper connection is normally discovered by testing the device before closing the patient's surgical wound. To test an implanted defibrillator, a test shock is given during sinus rhythm. To further test the device, fibrillation is then induced in the patient's heart, and the device is allowed to automatically detect the fibrillation and treat it with proper defibrillation therapy. If the device has a faulty lead connection and does not respond properly, a conventional defibrillator with external paddles is employed. External defibrillation carries risks that are preferably reduced by minimizing the number of bad connections. After a faulty connection is corrected, the test procedure is repeated. While somewhat reasonably effective, the existing connection techniques and apparatus have less than optimal certainty of connection, which can prolong the surgery and increase the risk to the patient. Also, a marginal connection may pass the initial test, but fail after implantation.
The preferred embodiment of the invention overcomes these limitations of the prior art by providing an implantable medical apparatus operable in conjunction with an attachable lead, and having a housing containing an electronic component, with a header connected to the housing and defining a cavity. A connector element is positioned within the cavity and is operably connected to the electronic component. A lens is connected to the header, such that the connector element may be viewed through the lens to facilitate confirmation of proper connection of a lead to the connector. The header may be transparent, and the lens or lenses either may be formed as part of the header, or may be detachable therefrom.